U.S. patent number 10,937,918 [Application Number 15/302,888] was granted by the patent office on 2021-03-02 for flexible printed circuit, and concentrator photovoltaic module and concentrator photovoltaic panel using same.
This patent grant is currently assigned to Sumitomo Electric Industries, Ltd.. The grantee listed for this patent is Sumitomo Electric Industries, Ltd.. Invention is credited to Shougo Asai, Kenichi Hirotsu, Takashi Iwasaki, Hiroyuki Matsuyama, Youichi Nagai, Kenji Saito.
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United States Patent |
10,937,918 |
Saito , et al. |
March 2, 2021 |
Flexible printed circuit, and concentrator photovoltaic module and
concentrator photovoltaic panel using same
Abstract
Provided is a flexible printed circuit including: a film-shaped
insulating base material having flexibility and having a withstand
voltage value of at least 2000 V; and an electric conductor layer
formed on the insulating base material and forming a circuit
pattern, wherein with respect to the insulating base material, a
principal component thereof is a polyimide and a filler content
thereof is 0%. Thus, a flexible printed circuit can be obtained
that has an insulating base material which suppresses decrease in
withstand voltage performance even in a high humidity
environment.
Inventors: |
Saito; Kenji (Osaka,
JP), Nagai; Youichi (Osaka, JP), Hirotsu;
Kenichi (Osaka, JP), Iwasaki; Takashi (Osaka,
JP), Asai; Shougo (Koka, JP), Matsuyama;
Hiroyuki (Joetsu, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Electric Industries, Ltd. |
Osaka |
N/A |
JP |
|
|
Assignee: |
Sumitomo Electric Industries,
Ltd. (Osaka, JP)
|
Family
ID: |
1000005396223 |
Appl.
No.: |
15/302,888 |
Filed: |
February 13, 2015 |
PCT
Filed: |
February 13, 2015 |
PCT No.: |
PCT/JP2015/053942 |
371(c)(1),(2),(4) Date: |
October 07, 2016 |
PCT
Pub. No.: |
WO2015/156028 |
PCT
Pub. Date: |
October 15, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170033249 A1 |
Feb 2, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 10, 2014 [JP] |
|
|
JP2014-081023 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L
31/048 (20130101); H01L 31/0543 (20141201); H01L
31/05 (20130101); H01L 31/049 (20141201); H05K
1/0257 (20130101); H02S 20/10 (20141201); H05K
1/028 (20130101); H05K 1/0373 (20130101); H05K
2201/0154 (20130101); Y02E 10/52 (20130101); H05K
1/0346 (20130101); H05K 2201/2009 (20130101); H05K
1/0393 (20130101) |
Current International
Class: |
H01L
31/05 (20140101); H05K 1/03 (20060101); H01L
31/054 (20140101); H01L 31/048 (20140101); H05K
1/02 (20060101); H02S 20/10 (20140101); H01L
31/049 (20140101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
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51-062691 |
|
May 1976 |
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JP |
|
52-122487 |
|
Oct 1977 |
|
JP |
|
05-025295 |
|
Feb 1993 |
|
JP |
|
06-220195 |
|
Aug 1994 |
|
JP |
|
2002-217508 |
|
Aug 2002 |
|
JP |
|
2006-083206 |
|
Mar 2006 |
|
JP |
|
2007-254643 |
|
Oct 2007 |
|
JP |
|
2008-218579 |
|
Sep 2008 |
|
JP |
|
2013-080760 |
|
May 2013 |
|
JP |
|
2013-149831 |
|
Aug 2013 |
|
JP |
|
2013-161867 |
|
Aug 2013 |
|
JP |
|
2011/111684 |
|
Sep 2011 |
|
WO |
|
2012165265 |
|
Dec 2012 |
|
WO |
|
2013/051426 |
|
Apr 2013 |
|
WO |
|
WO-2013114685 |
|
Aug 2013 |
|
WO |
|
Other References
English Translation WO2013114685 (Year: 2013). cited by examiner
.
Office Action in counterpart Japanese Patent Application No.
2010-081023, dated Sep. 1, 2016. cited by applicant .
Decision of Refusal in counterpart Japanese Patent Application No.
2014-081023, dated Feb. 2, 2016. cited by applicant .
International Search Report in International Application No.
PCT/JP2015/053942, dated Apr. 21, 2016. cited by applicant.
|
Primary Examiner: Gardner; Shannon M
Attorney, Agent or Firm: Baker Botts L.L.P. Sartori; Michael
A.
Claims
The invention claimed is:
1. A concentrator photovoltaic module comprising: a housing having
a planar bottom surface; a reinforcement portion which is
conductive and mounted to the planar bottom surface; a first
adhesive layer forming a constant thickness layer on the
reinforcement portion; a flexible printed circuit arranged in a
plurality of rows on the bottom surface; a concentrating portion
mounted to the housing and formed by a plurality of lens elements
being arrayed, each lens element being configured to converge sun
light; and cells mounted to the flexible printed circuit so as to
correspond to light-concentrating positions of the respective lens
elements, each cell being configured to receive the converged light
to generate power, wherein the flexible printed circuit includes: a
strip-film-shaped insulating base material having flexibility and
having a withstand voltage value of at least 2000 V; an electric
conductor layer formed on the insulating base material and forming
a circuit pattern; a lead frame of each of the cells mounted to the
electric conductive layer, a second adhesive layer which covers
both end faces of the electric conductive layer in a width
direction perpendicular to a longitudinal direction of the electric
conductive layer, and a cover layer which is provided on the second
adhesive layer, and with respect to the insulating base material, a
thickness thereof is in a range of 10 .mu.m to 50 .mu.m, a
principal component thereof is a polyimide, and a filler is
included, wherein the filler is any of calcium pyrophosphate,
calcium phosphate, or calcium carbonate, an upper-limit content of
the filler is 0.2% and excluding more than 0.2% to suppress
hygroscopicity of the insulating base material even after having
immersed the insulating base material in water, and external
surfaces of the cover layer, the second adhesive layer, the
insulating base material, and the first adhesive layer provide a
path for a current leak from the lead frame to the reinforcement
portion.
2. A concentrator photovoltaic panel formed by a plurality of the
concentrator photovoltaic modules being arranged, according to
claim 1.
Description
TECHNICAL FIELD
The present invention relates to a flexible printed circuit to be
used in a concentrator photovoltaic module which is a component of
a concentrator photovoltaic panel, for example.
BACKGROUND ART
A unit serving as an optical-system basic unit for concentrator
photovoltaic (CPV) generates power by guiding, to a small cell, a
light spot which is formed by light being converged by a
concentrating portion composed of a Fresnel lens. As the cell, a
solar battery having a high power generation efficiency is used.
With such a configuration, large optical energy can be concentrated
on a small cell, and thus, power can be generated at a high
efficiency. A large number of such units are arranged in a matrix
shape to form a concentrator photovoltaic module, and further, a
large number of the modules are arranged in a matrix shape to form
a concentrator photovoltaic panel. Such a concentrator photovoltaic
panel is caused to perform tracking operation by a drive device so
that the concentrator photovoltaic panel always faces the sun,
whereby highly-efficient power generation during day time can be
realized.
In one module, the cells are disposed so as to be in one-to-one
correspondence to a large number of Fresnel lenses. In addition,
each cell is mounted to a circuit board. Mounting all the cells on
one large substrate requires a very large substrate, and results in
difficult manufacturing and large cost. Meanwhile, by arranging
only a necessary number of substrates being made of a resin or the
like and having a size that allows easy manufacture thereof, and by
mounting a plurality of cells on each substrate, it is possible to
realize a configuration in which the cells by the same number of
Fresnel lenses as a whole are arranged in a matrix shape.
Further, from the viewpoint of reducing cost and improving heat
dissipation performance, a configuration is also conceivable in
which: instead of the substrate made of a resin or the like, a
strip-film-shaped (ribbon-shaped) flexible printed circuit having
mounted cells thereto is laid throughout on the bottom surface of
the housing of a module such that the cells are disposed at the
respective light-concentrating positions (see PATENT LITERATURE 1,
paragraph [0026], for example).
As an insulating base material for the flexible printed circuit, a
polyimide film is used in general (see PATENT LITERATURE 2 to 4,
for example). For easier handling of such a polyimide film through
provision of slidability thereto, the polyimide film has a filler
such as calcium phosphate added thereto. The added amount is
selected from the viewpoint of ensuring slidability.
CITATION LIST
Patent Literature
PATENT LITERATURE 1: Japanese Laid-Open Patent Publication No.
2013-161867
PATENT LITERATURE 2: Japanese Laid-Open Patent Publication No.
H6-220195
PATENT LITERATURE 3: Japanese Laid-Open Patent Publication No.
H5-25295
PATENT LITERATURE 4: Japanese Laid-Open Patent Publication No.
2006-83206
SUMMARY OF INVENTION
Technical Problem
When the flexible printed circuit is used in a weak current
apparatus, such as a mobile phone, for example, high withstand
voltage performance is not required in the flexible printed circuit
itself.
However, when the flexible printed circuit is used in a
concentrator photovoltaic module, there are cases where voltage of
several hundred to 1000 volts is applied due to a series connection
of the cell. In the case of such a system voltage (working
voltage), the required withstand voltage value is still higher, and
is 2 times+1000 V of the system voltage, for example. Therefore, if
the system voltage is 1000 V, the withstand voltage value becomes
3000 V.
Further, in the case of the concentrator photovoltaic module, since
the concentrator photovoltaic module is used outdoor where
temperature and humidity change to a great extent, there are cases
where the humidity inside the module becomes 100% or as high as
close to 100%, due to dewing or entry of rain. In such a state,
there are cases where the insulation performance of the insulating
base material in the flexible printed circuit is decreased and the
flexible printed circuit cannot withstand high voltage.
In view of the above conventional problem, an object of the present
invention is to provide a flexible printed circuit having an
insulating base material which suppresses decrease in withstand
voltage performance even in a high humidity environment, and to
provide a concentrator photovoltaic module and a concentrator
photovoltaic panel using the same.
Solution to Problem
The present invention is a flexible printed circuit including: a
film-shaped insulating base material having flexibility and having
a withstand voltage value of at least 2000 V; and an electric
conductor layer formed on the insulating base material and forming
a circuit pattern, wherein with respect to the insulating base
material, a principal component thereof is a polyimide and a filler
content thereof is 0%.
Moreover, the present invention is a flexible printed circuit
including: a film-shaped insulating base material having
flexibility and having a withstand voltage value of at least 2000
V; and an electric conductor layer formed on the insulating base
material and forming a circuit pattern, wherein with respect to the
insulating base material, a thickness thereof is in a range of 10
.mu.m to 50 .mu.m, a principal component thereof is a polyimide,
and a filler content thereof is not greater than 0.2%.
Moreover, the present invention is a concentrator photovoltaic
module including: a housing having a planar bottom surface; a
flexible printed circuit arranged in a plurality of rows on the
bottom surface; a concentrating portion mounted to the housing and
formed by a plurality of lens elements being arrayed, each lens
element being configured to converge sun light; and cells mounted
to the flexible printed circuit so as to correspond to
light-concentrating positions of the respective lens elements, each
cell being configured to receive the converged light to generate
power, wherein the flexible printed circuit includes: a
strip-film-shaped insulating base material having flexibility and
having a withstand voltage value of at least 2000 V; and an
electric conductor layer formed on the insulating base material and
forming a circuit pattern, and with respect to the insulating base
material, a principal component thereof is a polyimide and a filler
content thereof is 0%.
Moreover, the present invention is a concentrator photovoltaic
module including: a housing having a planar bottom surface; a
flexible printed circuit arranged in a plurality of rows on the
bottom surface; a concentrating portion mounted to the housing and
formed by a plurality of lens elements being arrayed, each lens
element being configured to converge sun light; and cells mounted
to the flexible printed circuit so as to correspond to
light-concentrating positions of the respective lens elements, each
cell being configured to receive the converged light to generate
power, wherein the flexible printed circuit includes: a
strip-film-shaped insulating base material having flexibility and
having a withstand voltage value of at least 2000 V; and an
electric conductor layer formed on the insulating base material and
forming a circuit pattern, and with respect to the insulating base
material, a thickness thereof is in a range of 10 .mu.m to 50
.mu.m, a principal component thereof is a polyimide, and a filler
content thereof is not greater than 0.2%.
Advantageous Effects of Invention
With the flexible printed circuit of the present invention, and the
concentrator photovoltaic module and the concentrator photovoltaic
panel using the same, it is possible to suppress decrease in the
withstand voltage performance of the insulating base material even
in a high humidity environment.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view showing one example of a concentrator
photovoltaic apparatus.
FIG. 2 is a perspective view (partially cut out) showing an
enlarged view of one example of a concentrator photovoltaic
module.
FIG. 3 is a cross-sectional view orthogonal to the longitudinal
direction in the flexible printed circuit shown in FIG. 2, and is a
cross-sectional view of the vicinity of a cell.
FIG. 4 is a schematic diagram showing a configuration of a
withstand voltage performance test.
FIG. 5 is a bar graph indicating, with respect to four kinds of
samples in three kinds of states, holding time [seconds] during
which a certain withstand voltage performance can be maintained
against an applied voltage of 3600 V.
FIG. 6 is a bar graph indicating, with respect to the four kinds of
samples in the three kinds of states, holding time [seconds] during
which a certain withstand voltage performance is maintained when
the applied voltage is raised to 4200 V.
FIG. 7 is a schematic diagram showing how to conduct a slidability
test.
FIG. 8 is a bar graph showing a result of the slidability test.
DESCRIPTION OF EMBODIMENTS
Summary of Embodiment
The summary of embodiment of the present invention includes at
least the following.
(1) This is a flexible printed circuit including: a film-shaped
insulating base material having flexibility and having a withstand
voltage value of at least 2000 V; and an electric conductor layer
formed on the insulating base material and forming a circuit
pattern, wherein with respect to the insulating base material, a
principal component thereof is a polyimide and a filler content
thereof is 0%.
In the flexible printed circuit configured as above, since the
insulating base material does not contain any filler, the
hygroscopicity can be suppressed at a low level. Thus, the
withstand voltage performance can be maintained at a high
level.
(2) This is a flexible printed circuit including: a film-shaped
insulating base material having flexibility and having a withstand
voltage value of at least 2000 V; and an electric conductor layer
formed on the insulating base material and forming a circuit
pattern, wherein with respect to the insulating base material, a
thickness thereof is in a range of 10 .mu.m to 50 .mu.m, a
principal component thereof is a polyimide, and a filler content
thereof is not greater than 0.2%.
When the filler content exceeds 0.2%, the higher the required
withstand voltage value is, the more significant the decrease in
the withstand voltage performance becomes due to moisture
absorption. However, with the flexible printed circuit configured
as above, the hygroscopicity can be suppressed at a low level by
making the filler content not greater than 0.2%. Thus, the
withstand voltage performance can be maintained at a high
level.
(3) This is a concentrator photovoltaic module including: a housing
having a planar bottom surface; a flexible printed circuit arranged
in a plurality of rows on the bottom surface; a concentrating
portion mounted to the housing and formed by a plurality of lens
elements being arrayed, each lens element being configured to
converge sun light; and cells mounted to the flexible printed
circuit so as to correspond to light-concentrating positions of the
respective lens elements, each cell being configured to receive the
converged light to generate power, wherein the flexible printed
circuit includes: a strip-film-shaped insulating base material
having flexibility and having a withstand voltage value of at least
2000 V; and an electric conductor layer formed on the insulating
base material and forming a circuit pattern, and with respect to
the insulating base material, a principal component thereof is a
polyimide and a filler content thereof is 0%.
With respect to the flexible printed circuit in the concentrator
photovoltaic module configured as above, since the insulating base
material does not contain any filler, the hygroscopicity can be
suppressed at a low level. Therefore, even when the state inside
the concentrator photovoltaic module becomes a high humidity state
due to dewing or the like, the withstand voltage performance of the
flexible printed circuit can be maintained at a high level.
(4) This is a concentrator photovoltaic module including: a housing
having a planar bottom surface; a flexible printed circuit arranged
in a plurality of rows on the bottom surface; a concentrating
portion mounted to the housing and formed by a plurality of lens
elements being arrayed, each lens element being configured to
converge sun light; and cells mounted to the flexible printed
circuit so as to correspond to light-concentrating positions of the
respective lens elements, each cell being configured to receive the
converged light to generate power, wherein the flexible printed
circuit includes: a strip-film-shaped insulating base material
having flexibility and having a withstand voltage value of at least
2000 V; and an electric conductor layer formed on the insulating
base material and forming a circuit pattern, and with respect to
the insulating base material, a thickness thereof is in a range of
10 .mu.m to 50 .mu.m, a principal component thereof is a polyimide,
and a filler content thereof is not greater than 0.2%.
When the filler content exceeds 0.2%, the higher the required
withstand voltage value is, the more significant the decrease in
the withstand voltage performance becomes due to moisture
absorption. However, with the flexible printed circuit in the
concentrator photovoltaic module configured as above, the
hygroscopicity can be suppressed at a low level by making the
filler content not greater than 0.2%. Therefore, even when the
state inside the concentrator photovoltaic module becomes a high
humidity state due to dewing or the like, the withstand voltage
performance of the flexible printed circuit can be maintained at a
high level.
(5) Moreover, a concentrator photovoltaic panel can be formed by a
plurality of the concentrator photovoltaic modules being arranged,
according to (3) or (4) above.
With this concentrator photovoltaic panel, even when the state
inside each concentrator photovoltaic module becomes a high
humidity state due to dewing or the like, the withstand voltage
performance of the flexible printed circuit can be maintained at a
high level.
Details of Embodiment
Concentrator Photovoltaic Panel and Concentrator Photovoltaic
Apparatus
First, a configuration of a concentrator photovoltaic apparatus
will be described.
FIG. 1 is a perspective view showing one example of a concentrator
photovoltaic apparatus. In FIG. 1, a concentrator photovoltaic
apparatus 100 includes: a concentrator photovoltaic panel 1; and a
pedestal 3 which includes a post 3a and a base 3b therefor, the
post 3a supporting the concentrator photovoltaic panel 1 on the
rear surface side thereof. The concentrator photovoltaic panel 1 is
formed by assembling a large number of concentrator photovoltaic
modules 1M vertically and horizontally. In this example, 62 (7 in
length.times.9 in breadth-1) concentrator photovoltaic modules 1M
except the center portion are assembled vertically and
horizontally. When one concentrator photovoltaic module 1M has a
rated output of about 100 W, for example, the entirety of the
concentrator photovoltaic panel 1 has a rated output of about 6
kW.
A drive device (not shown) is provided on the rear surface side of
the concentrator photovoltaic panel 1. By causing this drive device
to operate, it is possible to drive the concentrator photovoltaic
panel 1 in two axes of azimuth and elevation. Accordingly, the
concentrator photovoltaic panel 1 is driven so as to always face
the direction of the sun both in azimuth and elevation. At a place
in the concentrator photovoltaic panel 1 (at the center portion in
this example) or in a vicinity of the panel 1, a tracking sensor 4
and a pyrheliometer 5 are provided. The operation of tracking the
sun is performed on the basis of the tracking sensor 4, and the
position of the sun calculated from the time and the latitude and
the longitude of the installation place.
Concentrator Photovoltaic Module
FIG. 2 is a perspective view (partially cut out) showing an
enlarged view of one example of a concentrator photovoltaic module
(hereinafter, also simply referred to as module) 1M (however, a
shielding plate described later is not shown). In FIG. 2, the
module 1M includes, as main components: a housing 11 formed in a
vat shape and having a flat bottom surface 11a; a flexible printed
circuit 12 disposed so as to be in contact with the bottom surface
11a and in a plurality of rows; and a concentrating portion 13
mounted, like a cover, to a flange portion 11b of the housing 11.
The housing 11 is made of a metal.
The flexible printed circuit 12 is obtained by providing an
electric conductor layer forming a circuit pattern on a
strip-film-shaped insulating base material. On top of this, cells
21 and other electronic components are mounted. As each cell 21, a
solar battery having heat resistance and a high power generation
efficiency is used.
The concentrating portion 13 is a Fresnel lens array and is formed
by arranging, in a matrix shape, a plurality of Fresnel lenses 13f
(for example, 16 in length.times.12 in breadth, 192 in total) which
concentrate sun light. Such a concentrating portion 13 can be
obtained by, for example, forming a silicone resin film on a back
surface (inside) of a glass plate used as a base material. Each
Fresnel lens 13f is formed on this resin film. The total number and
the arrangement of the Fresnel lenses 13f are the same as the total
number and the arrangement of the cells 21, and the Fresnel lenses
13f and the cells 21 are in one-to-one correspondence with each
other so that their optical axes are aligned with each other. A
connector 14 for taking out the output of the module 1M is provided
on the external surface of the housing 11.
Configuration of Flexible Printed Circuit
FIG. 3 is a cross-sectional view orthogonal to the longitudinal
direction in the flexible printed circuit 12 shown in FIG. 2, and
is a cross-sectional view of the vicinity of the cell 21. It should
be noted that the shown thickness dimensions are merely examples.
Also, this figure is for schematic representation of the cross
sectional structure, and is not necessarily proportional to the
actual size.
In FIG. 3, the flexible printed circuit 12 includes: an insulating
base material 121 (thickness 25 .mu.m) made of a polyimide; an
electric conductor layer 122 (thickness 35 .mu.m) provided on top
of the insulating base material 121, made of copper, and forming a
circuit pattern; a solder portion 123 which connects a cell 21
packaged together with a lead frame 18 to the electric conductor
layer 122 via the lead frame 18; an adhesive layer 124 (maximum
thickness 60 .mu.m); and a cover layer 125 (thickness 25 .mu.m)
made of a polyimide. The insulating base material 121 has
flexibility and has a strip-film shape (ribbon shape extending in
the longitudinal direction). The flexible printed circuit 12, also
as a whole, has a thickness of about 110 .mu.m, has a
strip-film-shape, and has flexibility.
A reinforcement portion 16 (thickness 800 .mu.m) made of an
aluminium alloy is mounted to the lower surface of the insulating
base material 121, via an adhesive layer 15 (thickness 25 .mu.m).
The reinforcement portion 16 allows the flexible printed circuit 12
to have a certain rigidity, thereby facilitating handling during
mounting of the flexible printed circuit 12. In addition, the
reinforcement portion 16 also contributes to dissipation of heat
from the flexible printed circuit 12 to the bottom surface 11a of
the housing 11. The reinforcement portion 16 is fixed to the bottom
surface 11a (thickness 1000 .mu.m=1 mm) with a double-sided tape 17
(thickness 35 .mu.m) which has electric conductivity (which also
has good thermal conductivity).
The cell 21 is packaged together with the lead frame 18 for taking
out an output. The lead frame 18 is electrically and mechanically
connected to the electric conductor layer 122 via the solder
portion 123. The top and the periphery of the cell 21 and the
periphery of the lead frame 18 are covered with a transparent
silicone resin layer 19.
The potential of the bottom surface 11a of the housing 11 is
maintained at the ground potential. Therefore, the potential of the
reinforcement portion 16 mounted to the bottom surface 11a via the
electrically conductive double-sided tape 17 also is the ground
potential. A direct-current voltage generated through solar
photovoltaic power generation is applied to the electric conductor
layer 122. Accordingly, a current I.sub.dc caused to flow due to a
potential difference V.sub.dc between the electric conductor layer
122 and the reinforcement portion 16 needs to be suppressed to less
than a predetermined value I.sub.L of an allowable level
(I.sub.dc<I.sub.L) by means of the insulating base material 121
and the adhesive layer 15. As indicated by arrows in FIG. 3, for
example, the current leak includes a current leak L1 which
penetrates the insulating base material 121 and the adhesive layer
15, a current leak L2 caused by a void (not shown) in the adhesive
layer 15 locally reducing the withstand voltage value, and a
current leak L3 which flows from the lead frame 18 on the external
surface against insulation.
Relationship Between Filler for Insulating Base Material, and
Withstand Voltage Performance and Slidability
The present inventors examined what change appears in withstand
voltage performance and slidability by changing the content of a
filler contained in the insulating base material 121 whose
principal component is a polyimide. Hereinafter, the examination
result will be described in detail. As the filler, calcium
pyrophosphate was used.
As the filler, calcium phosphate, calcium carbonate, and silica are
also appropriate, other than calcium pyrophosphate. However, here,
as a representative, a case where the filler was calcium
pyrophosphate was examined.
The kinds of the insulating base material 121 used in the
examination are shown in table 1. Here, with respect to the
thickness of the insulating base material 121, the nominal value is
25 .mu.m, and the measured value is also approximately 25
.mu.m.
TABLE-US-00001 TABLE 1 Article Article Conventional containing
containing Non- article filler by 0.2% filler by 0.1% filler
Nominal 25 25 25 25 thickness [.mu.m] Measured 24.9 24.8 25.0 24.8
thickness [.mu.m]
It is preferable that the thickness of the insulating base material
121 is in the range of 10 .mu.m to 50 .mu.m (not less than 10 .mu.m
and not greater than 50 .mu.m). When the thickness is less than 10
.mu.m, it becomes difficult to ensure a necessary withstand voltage
value. When the thickness exceeds 50 .mu.m, it becomes difficult to
ensure a necessary thermal conductivity (heat dissipation
performance). The thickness 10 .mu.m to 50 .mu.m for the insulating
base material 121 is a preferable range for realizing both the
necessary withstand voltage value and the necessary thermal
conductivity.
The concept regarding the withstand voltage is as follows according
to the IEC standard (62108, 62688).
The withstand voltage performance in the case of grade A is being
able to withstand (system voltage.times.4)+2000 V for two
minutes.
The withstand voltage performance in the case of grade B is being
able to withstand (system voltage.times.2)+1000 V for two
minutes.
The system voltage is 500 to 1000 V in general, and a target
therefor can be 500 V, 600 V, or 1000 V, for example.
When the system voltage is 1000 V, the withstand voltage value for
grade A is 6000 V, and the withstand voltage value for grade B is
3000 V.
When the system voltage is 600 V, the withstand voltage value for
grade A is 4400 V and the withstand voltage value for grade B is
2200 V.
When the system voltage is 500 V, the withstand voltage value for
grade A is 4000 V, and the withstand voltage value for grade B is
2000 V.
Therefore, an insulating base material for a flexible printed
circuit to be used in a concentrator photovoltaic module is
required to have insulation performance capable of withstanding at
least 2000 V, preferably 3000 V or greater. When the system voltage
is 1000 V, the withstand voltage for grade B is 3000 V.
FIG. 4 is a schematic diagram showing a configuration of a
withstand voltage performance test. The test condition was as
follows. An insulating base material 121s serving as a sample
(hereinafter, simply referred to as sample) was interposed between
disc electrodes P and N each having a diameter of 20 mm, and then,
direct-current voltage was applied. The applied voltage was 3600 V,
and the step-up condition was 500 V/sec. The time period during
which 3600 V was applied was 300 seconds at maximum. The sample was
prepared in three states in which:
(a) the sample in an ordinary state (not immersed in water);
(b) the sample immediately after being taken out of pure water
where the sample has been immersed at 23.degree. C. for 10 hours;
and
(c) the sample immediately after being taken out of pure water
where the sample has been immersed at 23.degree. C. for 24
hours.
The sample itself was prepared in four kinds:
(1) conventional article (filler content 2%);
(2) article having filler content of 0.2%;
(3) article having filler content of 0.1%; and
(4) non-filler article that does not contain any filler (filler
content 0%)
It should be noted the contents above are expressed in mass %.
FIG. 5 is a bar graph indicating, with respect to the four kinds of
samples in the three kinds of states (a), (b), and (c) defined
above, a time period until a current leak I.sub.dc, (?I.sub.L) not
less than a predetermined value I.sub.L is detected under the
applied voltage of 3600 V, i.e., holding time [seconds] during
which a certain withstand voltage performance can be maintained. In
FIG. 5, in the case of "(a) ordinary state" i.e., non-immersion in
water, all samples attain 300 seconds. However, in the case of "(b)
10 hours", with respect to the conventional article sample (1), the
holding time is considerably decreased and is far from the
specification value (120 seconds). With respect to other samples
(2) and (3), the holding time is slightly decreased but satisfies
the specification value. With respect to non-filler sample (4), the
holding time is not decreased.
Further, in the case of "(c) 24 hours", with respect to the
conventional article sample (1), the holding time is further
decreased, and is far from the specification value (about 120
seconds). Also with respect to other samples (2) and (3), the
holding time is further decreased, but still satisfies the
specification value. With respect to the non-filler sample (4),
decrease in the holding time is not observed.
When summarizing the result shown in FIG. 5, with respect to "(1)
conventional article", it is seen that after the immersion in
water, the withstand voltage performance against the applied
voltage 3600 V is considerably decreased and does not satisfy the
specification value. With respect to "(2) filler 0.2%" and "(3)
filler 0.1%", the withstand voltage performance is decreased in
accordance with the time period of the immersion in water, but
satisfies the specification value. With respect to "(4)
non-filler", even after the immersion in water, the withstand
voltage performance is not decreased.
That is, in terms of the withstand voltage performance in the case
of the immersion in water performed, "non-filler" is best, followed
by "filler 0.1%" and then by "filler 0.2%", in this order, and
"conventional article" is not appropriate.
FIG. 6 is a bar graph indicating, with respect to the same four
kinds of samples as in FIG. 5 in the same three kinds of states
(a), (b), and (c) defined above, the holding time [seconds] during
which a certain withstand voltage performance is maintained when
the applied voltage is raised to 4200 V. This can be said as an
examination for confirming how change in the holding time appears
when an intentionally-raised voltage is applied.
Here, with respect to all the samples, the holding time after the
immersion in water shows decrease when compared with that in "(a)
ordinary state". However, with the extent of the decrease focused,
when the holding time after the immersion for 24 hours relative to
the holding time in the ordinary state is expressed in the rate
[%], "(1) conventional article" exhibits 13%, "(2) filler 0.2%"
exhibits 56%, "(3) filler 0.1%" exhibits 65%, and "(4) non-filler"
exhibits 89%.
That is, in the viewpoint of suppressing decrease in withstand
voltage performance after immersion in water, "non-filler" is best,
followed by "filler 0.1%" and then "filler 0.2%", in this order,
and "conventional article" is inferior.
From the result above, the following conclusion can be derived.
First, the target is an insulating base material for a flexible
printed circuit, the insulating base material having a withstand
voltage value of at least 2000 V. As such an insulating base
material, if an insulating base material whose principal component
is a polyimide and whose filler content is 0% (non-filler) is used,
it is possible to suppress the hygroscopicity at a very low level
because the insulating base material does not contain a filler.
Thus, the withstand voltage performance can be maintained at a high
level. In addition, even when the state inside the concentrator
photovoltaic module becomes a high humidity state due to dewing or
the like, the withstand voltage performance of the flexible printed
circuit can be maintained at a high level.
Also, even when the insulating base material is not a "non-filler",
if an insulating base material is used whose thickness is in the
range of 10 .mu.m to 50 .mu.m, whose principal component is a
polyimide, and whose filler content is not greater than 0.2%, the
hygroscopicity can be suppressed at a low level. Thus, the
withstand voltage performance can be maintained at a high level. In
addition, even when the state inside the concentrator photovoltaic
module becomes a high humidity state due to dewing or the like, the
withstand voltage performance of the flexible printed circuit can
be maintained at a high level. It should be noted that, if the
filler content exceeds 0.2%, as shown by the "(2) filler 0.2%"
sample in FIG. 6, decrease in the withstand voltage performance
becomes significant due to moisture absorption. The "(2) filler
0.2%" sample satisfies the necessary withstand voltage performance
in FIG. 5, but does not satisfy the withstand voltage performance
when the voltage is increased to 4200 V, and thus, can be
considered as the upper limit line for preferable content. That is,
it can be considered that 0.2% is the upper limit for the
filler.
Next, FIG. 7 is a schematic diagram showing how to conduct a
slidability test. The sample is obtained by forming a copper foil
on an insulating base material made of a polyimide (P1). In FIG. 7,
the respective materials are represented by hatchings having
different directions. From a stationary state where the two
samples, i.e., the polyimide insulating base materials, are in
contact with each other under a load (weight 200 g on 64
cm.sup.2=80 mm.times.80 mm), a force F for moving the upper sample
in the arrow direction is applied. This force F is proportional to
the friction force at surface contact between the insulating base
materials. The larger the value of F is, the worse the slidability
is, and the smaller the value of F is, the better the slidability
is.
FIG. 8 is a bar graph showing a result of the slidability test. The
value 1.8 of F in the vertical axis is the value of a general
polyimide film. From this graph, it is seen that "conventional
article", "filler 0.2%", and "filler 0.1%" have slidability
equivalent to or greater than or equal to the slidability of the
general polyimide film, but "non-filler" does not have good
slidability.
When the slidability is not good, the insulating base materials
easily adhere to each other, which poses a defect of difficult
handling thereof. However, if the insulating base material is
attached to the reinforcement portion 16 (FIG. 3), this defect is
not so troublesome. Therefore, for usage that requires a withstand
voltage performance not less than 2000 V, even if slidability is
sacrificed to some extent, it is overwhelmingly meaningful to
ensure a withstand voltage performance obtained by employing a
non-filler insulating base material or by suppressing the filler
content to not greater than 0.2%.
It should be noted that the embodiment herein is to be considered
in all respects as illustrative and not restrictive. The scope of
the invention is indicated by the appended claims, and all changes
which come within the meaning and range of equivalency of the
claims are therefore intended to be embraced therein.
REFERENCE SIGNS LIST
1 concentrator photovoltaic panel 1M concentrator photovoltaic
module 3 pedestal 3a post 3b base 4 tracking sensor 5 pyrheliometer
11 housing 11a bottom surface 11b flange portion 12 flexible
printed circuit 13 concentrating portion 13f Fresnel lens 14
connector 15 adhesive layer 16 reinforcement portion 17
double-sided tape 18 lead frame 19 silicone resin layer 21 cell 100
concentrator photovoltaic apparatus 121, 121s insulating base
material 122 electric conductor layer 123 solder portion 124
adhesive layer 125 cover layer
* * * * *